CS488 - Introduction to Computer Graphics - Lecture 22
Comments and Questions
- Exam: April 16th, 2008, 09.00, RCH???
Colour
Light
Almost all the effects are effects of energy
- Coherence is not an issue
Light is both a particle and a wave
Geometry
Light travels in straight lines
- except when it doesn't
- Then we re-define `straight line'.
Light travels fast
- about one foot per nansecond
- with respect to what
Particles
The easiest way to think about light.
Particles have a property
- wavelength (\lambda) or frequency (\nu)
- perceived differently depending on this property
- we call the difference `colour'
Waves
`Wavelength' suggests waves.
Actually two competing theories
- corpuscular theory (Newton)
- wave theory (Huyghens)
Two hundred years ago the wave theory won.
- Young's experiment
- depends on coherence
- Maxwell put the icing on the cake
One hundred years ago a compromise solution was found
Colour
Colour is the first application of linear algebra.
Grassmann: We don't know what colour is but we know it has certain
properties. Let's build a formal system with the properties and see what
comes out.
- Focus on matching
- Two colours `are the same' if the `look the same'.
- Focus on additive mixture
- Build colours by adding - in the sense of adding light.
- Observe linearity
- Changing intensity
- Adding two lights
- How many primaries?
- You need subtraction
So we now have a formal model of colour
- Choose three standard primaries
- Express a colour in terms of the primaries
- You can reproduce it exactly
Expressing a colour in terms of the primaries
- The colour matching experiment
In practice, the `colour gamut' is an issue
Models of Colour in Computer Graphics
Have an output device with three primaries
- Express the colour in terms of those primaries
- You need to do a change of basis, which you know well how to do.
- But first you need to calibrate the device, which you may not know how
to do.
Natural Phenomena
The General Idea
Human Skin
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